Since a number of years designers of piston combustion engines have seen a need of being able to vary the valve times during engine operation, since this would result in great advantages with regard to, for example, fuel economy and emissions.
Therefore, extensive efforts have been made in order to replace conventional camshaft systems for the opening and closure of engine valves by systems that are based on the use of electromagnetism for controlling and operating the valves of the engine. The disadvantage of such solutions is that the high requirements on the speed by which the valves can be operated will result in high requirements on the electromagnets that are used. The mass that each electromagnet has to bring into motion corresponds to the mass of the valve. The valve must comprise a suitable magnetic material in order to be displaced by the action of one or more electromagnets, and such materials contribute to an increase of the mass of conventional valves. This often results in an evil circle in which an improvement of a valve from a magnetic point of view will result in a weight increase that, in its turn, results in a need of larger and more powerful electromagnets. Accordingly, in this way, it will be difficult to achieve an economically and practically good solution to obtaining a sufficiently fast control and operation of the valves of the engine. Moreover, it is well known that electromagnets will require a certain time for magnetising and demagnetising.
There are also efforts being made to obtain the requested movements of the engine valves by means of hydraulics. Today, such systems are tested by, amongst others, vehicle manufactures. The pressure fluid, here the hydraulic liquid, is in this case used in order to effect the engine valve movement. Thereby, it is required that the pressure pulse generator that is used has an ability to deliver the pressure pulses that cause the valve movements rapidly and with high precision. The present inventor does not know any pressure pulse generator according to prior art that has the performance required to satisfyingly cope with the valve control at the rotations per minute of the engine that are used today in two-stroke, and, in particular, four-stroke combustion engines. An obstacle to the accomplishing of such a pressure pulse generator may be the difficulty to achieve sufficiently rapid opening/closure movement of the valve or valves that is/are required in such a pressure pulse generator. Here, it should be mentioned that valves are often replaced by ports in modern two-stroke engine constructions, but that the present invention results in the possibility of using valve technology in two-stroke engines in a way corresponding to that of four-stroke engines.
In this context, it should also be mentioned that the pressure pulse generators that may come in question should be compact and occupy only a small space in combustion engine applications.